1. Field of the Invention
The disclosure relates generally to wireless communication systems and methods for processing handover messages thereof, and more particularly, to methods and systems for processing handover messages of wireless communication systems that includes a femtocell and a macrocell to achieve seamless handover between the femtocell and the macrocell and implement a local call switch function.
2. Description of the Related Art
Universal Mobile Telecommunications System (UMTS) is one of the third generation (3G) mobile communication technologies, which is evolved from Global System for Mobile communication (GSM), and it mainly adopted the use of GSM core network (referred to as CN) and a new Wideband Code Division Multiple Access (WCDMA) technology to provide user higher wireless transmission rate and better mobile services. In order to be able to provide a more simple communication environment and excellent communication quality in the home or business office environment, the concept of femtocell (also known as home base station) has been proposed.
Femtocells or so-called home base stations are designed to take advantage of a broadband cable network services in a small company or home to improve the problem of poor coverage, which utilizes the femtocell base station (HomeNode B, hereinafter referred to as HNB) as the near end of the wireless access network, and the broadband cable networks to connect to the core network of a ISP at its back end, to provide the user equipment (hereinafter referred to as UE) to access mobile internet services including circuit switching and packet switching services via the femtocell base stations (Femto AP or HNB). HNB may be designed simpler than most of general base stations, using less power, whether from the outdoor to indoor, or indoor to outdoor, only the same UE may be utilized, without complicated device switching or mode switching operations. In addition, the HNB may further effectively reduce the overhead and spectrum resources of the external base stations since the transmission overhead from the home and office users can be distributed to various femto base stations or femto access points (FAPs). Because most of the HNB applications may be applied in the home and enterprise, a local call switch function based on the femtocell and base station is derived. Through the local call switch function, the communication between two UEs configured with same femto gateway can be directly transferred by the femto gateway, without the need to pass a signal to the core network behind of the femto gateway back end. Through the forwarding of the femto gateway, after a voice connection is established, voice streams of the users may be directly exchanged in the femto gateway, thus not entering the core network for processing, so that data packets do not enter the core network. Therefore, the overhead of core network can be reduced.
However, a handover operation may be performed for the 3G system user due to fading in signal, so in the implementation of local call switch in the femtocell, the following two problems may be encountered.
First, when using the local call switch function, the control message of call setup will not enter the core network, so when the local call switch function is enabled, due to the core network does not contain information about the call, if the user needs to handover to the macro network (Referred to as MN) of the base station, a call interrupt phenomenon may be occurred. In addition, if a femtocell user and a macro network user are communicating with each other and the macro network user moves into the scope of HNB to result in a handover to the femtocell to occur, although local call switch conditions is met, it can not use the local call switch function due to the call being established by the core network.